According to the documentation it has to be inet:hostname() which is string(), which in elixir means char_list, so your hostname has to be 'example.com'. Alternatively you can also use the c-sigil (~c[example.com])

notice the single quotes ' instead of double "

Generally when interacting directly with Erlang libs, they expect char lists

Thanks, @NobbZ – you’ve solved a problem of mine yet again!

You should mark this thread as solved so others can see the answer right away and see it as solved in the thread list.

Just small note that from Elixir 1.5 you should use String.to_charlist and previous version - to_char_list is deprecated.

@NobbZ I actually looked in the docs and didn’t see this solution. Is it mentioned somewhere on this page: gen_tcp — OTP 29.0.2 (kernel 11.0.2) ? Are these the docs you were referring to?

Yes, they are.

The spec of :gen_tcp.connect/3:

connect(Address, Port, Options) → {ok, Socket} | {error, Reason}

Types

• Address = inet:socket_address() | inet:hostname()
• [other types omitted since they are unimportant here]

inet:hostname() (which is :inet.hostname in elixir syntax) is defined as follows:

hostname() = atom() | string()

Erlangs string() type is equal to elixirs charlist type.

charlists can be created using the charlist literal, which is an single-quoted “string”. Also one can use the c and C sigils to create them, when one wants to be a little bit more explicit.

And as @PatNowak correctly tells, you can convert anything implementing List.Chars by passing it to Kernel.to_charlist/1

thanks - seems so obvious now.